Contacting the Ning tech support, I found out that Ning doesn't support Mac uploads from Safari, but does (seem to) work with Firefox (although the pop-up window looks a bit buggy).
I tested it with an arrangement I made from the harpsichord music of J. H. Roman. http://earlyguitar.ning.com/profile/RockyMjos -- Rocky -- To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
